1. Field of the Invention
The present invention relates to a digital data transmission method for transmitting digital data such as depth data for digital image processing apparatus in a transmission format which has a bit number which is smaller than the original bit number for this digital data.
2. Description of the Prior Art
In the prior art, digital data such as depth data for digital image processing apparatus has been expressed using at least 20 bits. Digital video data, on the other hand, has been expressed using 10 bit digital data, a number which is smaller than the number for the depth data. Transfer formats for transferring 10 bit digital video data have therefore been put forward.
This 10 bit digital video data is described using 1024 (2.sup.10) values from 000h to 3FFh. Here, h indicates that the numeric value which preceded h was hexadecimal However, in this digital video data transmission format, the four values from 000h to 003h and the four values from 3FCh to 3FFh, giving a total of 8 values, are used to correspond to forbidden codes. These forbidden codes are used for the transmission of information such as control information and information other than picture data. It follows that the values which can be used to correspond to codes for picture data in the digital video data are the 1016 codes ranging from 004h to 3FBh.
Various benefits such as the common use of transmission control equipment can be enjoyed if 20 bit digital data such as depth data can be transmitted in accordance with the transmission format for this kind of 10 bit digital data. According to the transfer format for 10 bit digital data, digital data of 20 bits or greater such as the depth data would have to be divided every 10 bits to be transmitted i.e. if the data to be transmitted consists of 20 bits, this would have to be divided into two items of 10 bit upper and 10 bit lower digital data.
However, if the 20 bit digital data is split up every ten bits, it is possible that one or both items of 10 bit digital data V2 and V1 may correspond to the forbidden codes. As these forbidden codes correspond to specific meanings, even if they are transmitted, their meaning will not correspond to that of the original data and mistakes will be made.
In the prior art, when transferring 20 bit digital data in accordance with the transmission format for 10 bit digital data which has forbidden codes, a limiter is used so that the forbidden codes are not transmitted i.e. the upper bits would be kept without the values 000h to 003h and 3FC to 3FF by a limiter.
However, if a limiter is also used to cut the forbidden codes from the lower bits, the value corresponding to the transmitted data is no longer continuous. That is if data from 3FCh to 003h in the lower bits is limited, with regards to the transmitted 20 bit digital data, the value following 01FFBh comes to be expressed as 02004h, and the value following 02FFBh comes to be expressed as 03004h, so that the values 01FFCh to 02003h, 02FFCh to 03003h and 03FFCh to 04003h become lost.
In the above, 20 bit data is divided up every 10 bits to be transmitted in accordance with the transmission format for 10 bit data having forbidden codes. This is done as if the lower bits not contain the forbidden codes i.e. even if there is an forbidden code in the lower 10 bits it is still just treated as usual data. However, as this runs contrary to the transmission format, it is not possible to use this lower bit digital data in the same way as digital video data.
Also, one bit of the lower bits can be used for the prevention of the generation of forbidden codes. For example, the most significant bit of the lower bits could be used for this purpose instead of for data, so that the data from the second most significant bit onwards could then be used for data so that it would no longer be possible to get forbidden codes in the lower bits. This would, however, mean that it would now be possible to only transmit the number of values which could be represented by 19 bits of digital data (2.sup.19). The resolution provided by 19 bits would not be sufficient for transmitting data such as depth data.
As the present invention sets out to solve these kinds of problems, its object is to provide a digital data transmission method in which a transmission format having forbidden codes transmits a predetermined number of bits at a time (i.e. 10), in such a manner that when digital data having a number of bits which is larger than the predetermined bit number in the transmission format (i.e. 20) is handled, this digital data can be transmitted efficiently and accurately in accordance with the transmission format.